1. Field of the Invention
The invention relates in general to monitoring methods useful in servicing complex systems, and more specifically to methods of monitoring an operating elevator system for the detection of malfunctions related to sequentially performed functions.
2. Description of the Prior Art
The control for elevator systems is complex due to the large number of different functions which are controlled, and due to the many different interrelationships between the functions. Some types of elevator system malfunctions are not detectable by "freezing" the system at any predetermined instant and observing the conditions of certain signals at that instant. For example, the malfunction may be an out-of-sequence operation; or, an operation, while properly sequenced, may not be performed at the correct time relative to the other functions of the sequence. Furthermore, such malfunctions may occur only intermittently, making direct observation difficult and time consuming. Thus, it would be desirable to provide a new and improved method of detecting such malfunctions, which method should be universal and flexible enough to enable it to be applied to any selected portion of an elevator system.